Device for dewatering suspensions

ABSTRACT

A device for dewatering suspensions such as sludge or similar dewaterable goods contains several rollers and filtering webs that follow a sinuous path around the rollers. The width of at least one pressure gap, as well as the force which is applied on the goods to be filtered in this pressure gap, may be adjusted by sliding or swivelling so that the ratio between linear pressure and surface pressure can be adapted to the properties of the goods to be dewatered. By influencing this ratio it is possible from a standard model to cover a wide range of applications by simple and economic means, so that the cost-effectiveness ratio is improved.

BACKGROUND OF THE INVENTION

The invention relates to a device for dewatering suspensions, such assludge or similar materials which can be dewatered, having a pluralityof rollers and two filter bands which are guided around the rollers inan S-shape and enclose the material to be dewatered between them.

It relates in particular to presses with a multitude of pressurerollers, wherein successive drying of the suspension by means of theS-shaped wrapping of the rollers by the filter bands is achieved with anincrease in rollers.

Such presses are employed in multitudinous designs, they are allessentially differentiated by the relative association of the successiverollers, their diameter and type of construction and the way of guidingthe bands around the rollers, in particular the size of the wrap angleof the filter bands around the individual rollers.

The suspension to be dewatered varies, depending on the area of use, andit is possible to dewater various sludges, such as communal sludge,which in turn show a more or less high degree of previous water removal.The pressing of fruits or parts of fruits is also performed with suchfilter presses.

In the course of this it has been shown that a certain type of press,i.e. a press with a defined roller configuration and filter bandguidance, will as a rule achieve an optimal operational result, i.e.generally a maximum degree of drying with specific suspensions or withspecific suspension compositions. Thus, the multitude of structuralvariants of such presses which are available in the marketplace as arule also are used to achieve optimum pressing results for specific orspecifically set suspensions, whose degree of pre-drying,macro-molecular structure, possibly with the addition of additives, lieswithin a defined range.

However, the planning and construction of specific press configurationsis increasingly elaborate, and such presses are relatively expensivebecause of the "specialist properties" described.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a press of thesimplest construction which covers a wide use spectrum by means ofsimple, quick and thus cost-effective modifications in construction,i.e. that a universally employable press is created by means of a simplebasic design of the device in accordance with the invention, which overa wide range provides optimal suspension dewatering with a particularlygood cost/benefit ratio.

This object is attained in accordance with the invention in that adevice as described at the outset includes a plurality of rollers andtwo filter bands for enclosing the suspension, the two filter bandsbeing guided along an S-shaped path around the rollers so that eachroller is contacted by one of the bands over a respective contact area,the improvement wherein: the plurality of rollers comprise at least onepair of rollers composed of first and second roller; and the devicefurther comprises at least one displacement mechanism coupled to one ofthe rollers of the at least one pair, the displacement mechanism beingmovable to displace the one of the rollers of the at least one pairrelative to the other one of the rollers of the at least one pair over apath to create a pressing gap of adjustable width between the first andsecond rollers and a pressing force of adjustable magnitude on thesuspension, whereby movement of the displacement mechanism creates anadjustable relation between the dewatering produced in the pressing gapand the dewatering produced in the contact area.

The basic concept of the invention therefore essentially consists inthat a basic component of the press consists of a pair of rollers whichcan be adjusted in relation to each other and which comprise a pressinggap between them. The wrap angle of both rollers of the roller pair ispreferably selected to cover 180°.

Such a roller pair allows the simultaneous use of both linear pressingand area pressing for dewatering the suspension, wherein, by means ofthe adjustable association with each other of the rollers of the rollerpair, both the absolute value of this pressing effect and also the ratiobetween linear pressing and area pressing can be simply set over a widerange.

It has been shown that, depending on the material to be dewatered,specific combinations of linear pressing/area pressing lead to anoptimal pressing result, i.e. to a maximum degree of drying. Thiscombination need not be the same for all degrees of drying of thepreviously dewatered material, i.e. even with a predetermined suspensionit may be necessary, for example, to vary the mentioned ratio of linearpressing/area pressing with the increasing degree of dryness of thesuspension when passing through several roller pairs, for example in thesense that with an increasing degree of dryness linear pressing plays anincreasing role, while area pressing moves into the background, or viceversa.

These possibilities of adjustment to the "dewatering characteristics" ofthe material of interest or the respective suspension permit anoptimization of the pressing result after each roller pair, so thatinstead of the multitude of rollers provided up to now, three pairs ofrollers already lead to very good pressing results for a large portionof industrial or communal applications, which particularly highlightsthe efficiency of the device in accordance with the invention.

It is of course also possible to place other, known roller arrangementsupstream or downstream of arrangements of such pairs of rollers, ifspecific jobs require this.

In accordance with a preferred design, the pressing gap and the linearpressure exerted by it are set with the aid of a force-actuated pivotarm on which the one roller is held, while the other roller can betangentially displaced and fixed in place, by means of which the wrapangle and thereby the area pressure, which the two rollers exert in thewrap area on the material to be dewatered, can be set.

However, the variable force actuation of the roller can also simply takeplace by means of a suitable presetting of the band tension of thefilter bands, if a suitable torque is generated on the pivot arm bythis.

Several such pairs of rollers can be disposed on a common frame,however, separate structural units can also be employed which arerespectively equipped with pivot arms and displacement options for thetwo rollers, so that such structural units or structural modules can beeasily mounted in suitable frames or holding devices of the press andcan again be removed, so that in this way an adaptation to the specificdewatering problem is possible with a few manipulations.

A plurality of further advantageous embodiments ensues from thedependent claims. Several such embodiments will now be described indetail with reference to of the drawings.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a lateral view of a press with a first preferred arrangementof roller pairs,

FIG. 2 is a schematic representation of the basic possible setting ofthe two rollers of a roller pair in relation to each other,

FIG. 3 is a lateral view of a further example with the inlet rollerlifted off for canceling the pressing gap,

FIGS. 4 to 10 are lateral views of devices in accordance with theinvention with at least two roller pairs and additional devices fordewatering,

FIG. 11 is a front view of a press in the feeding area for the materialto be pressed.

FIG. 12 is a perspective view of an alternative form of construction ofthe feeding area of a press according to the invention.

The press shown in FIG. 1 in section or a lateral view consists in thecustomary manner of an upper filter band 80 and a lower filter band 90,which are respectively endlessly guided over a plurality of pressurerollers and reversing rollers. The constructive steps for guiding thesefilter bands individually and for their tension are known from the priorart and need not be described here.

The (possibly pre-dewatered)) material to be pressed is placed on thelower filter band 90 in a feeding station AF, and is subsequently guidedthrough a combination of three pairs of pressing rollers 10, 20, 30, andfinally the dewatered material is discharged in a release station AG andconveyed away by suitable means.

Each one of the roller pairs 10, 20, 30 consists of an upper roller . .. A and a lower roller . . . B. In the exemplary embodiment represented,the respectively upper roller . . . A is held on a pivot arm 12, 22, 32,whose one end is connected with the upper frame 50 of the press (notshown), and whose other end is engaged by a device 41, 42, 43 (forexample a hydraulic cylinder), which is also fastened on the upper frame50, and with the aid of which the upper roller . . . A can be pivoted inrespect to the respectively lower roller . . . B, wherein in particularthe distance between the two rollers, and with it the pressing gap forthe two filter bands 80, 90 passed between the two rollers, is defined.

Each one of the lower pressing rollers . . . B can be horizontallydisplaced by means of suitable horizontal guides, not shown in FIG. 1,i.e. in a direction essentially tangentially in respect to therespectively upper pressing roller . . . A. With the solutionsrepresented in FIG. 1 and the subsequent exemplary embodiments, wrapangles of the filter bands around each roller of at least 180° have beenselected in this case. An additional drying band 60 is associated withthe last pressing roller pair 30, for example a felt band, as well as anadditional drying roller 95. The drying band 60 is used to removeresidual moisture on the filter band 80, the drying roller 95 forremoving residual moisture from the underside of the filter band 90.

The exemplary embodiment represented is an essentially horizontallyoperating press, however it can be easily seen that it is also possibleto displace the entire press or the arrangement of the roller pairs 10,20, 30 as a whole or partially into the vertical, depending on how thespatial requirements in the actual case of application demand it.

FIG. 2 shows the mode of functioning of the two rollers of a roller pairschematically by means of the example of the upper pressing roller 10Aand the lower pressing roller 10B of the first roller pair 10. In theposition of the two rollers 10A, 10B shown in solid lines they areessentially located above each other, i.e. the angle α (not drawn in forthis position) of the connecting line X2--X2 of the axes of these tworollers in respect to the horizontal (the frame 40 in FIG. 1) isapproximately 90° here, the two positions of the lower pressing roller10B shown in dashed lines indicate extreme positions, wherein therespective connecting lines X1--X1 or X3--X3 form an angle of 150° or40° with the horizontal. Wrap angles of the two filter bands of morethan 180° around both pressing rollers occur in the by far greatestadjustment range of these angles. The pivot arm 12 is only shownschematically here, as well as the device 41 in the form of a cylinderwhich acts with a force on the pivot arm 12, and in this way the upperpressing roller 10A can be pivoted on a section of an arc in thedirection of the two-headed arrow, wherein the seating of the pivot arm12 has been selected such that positions such as shown in FIG. 2 can beset by operating the pivot lever, wherein the upper pressing roller 10Ais seated on the lower pressing roller 10B with practically a gap of 0,as well as positions, such as represented in FIG. 3, wherein the upperpressing roller 10A is lifted off the lower pressing roller 10B andtherefore no pressing gap is defined anymore between these two rollers.In the last mentioned exemplary embodiment in accordance with FIG. 3,the positioning of the lower pressing roller 10B shown in dashed linesindicates that in such an operational case the displacement of the lowerpressing roller 10B exclusively leads to a setting of the wrap angles ofboth rollers.

The suspended mounting, which can be force-defined, of the upperpressing roller 10A in connection with the essentially tangentialdisplacement of the lower pressing roller therefore results in amultitude of relative positions of these two pressing rollers in respectto each other, with the possibility resulting therefrom of presetting inthe simplest manner the combination of area pressing and linear pressing(pressing gap) required for every material to be pressed in everypressing stage.

In connection with FIGS. 4 to 10, only concrete examples of use andpreferred exemplary embodiments of arrangements of pressing roller pairsin accordance with FIGS. 2 and 3 are provided:

FIG. 4 shows the arrangement of three pairs of pressing rollers (thesecould be the pressing roller pairs shown in the press in FIG. 1, forexample), wherein in this case the two outer pressing roller pairs areoperated with a minimal pressing gap, the center pressing roller pair20A, 20B without a pressing gap; this arrangement represents a certainamount of careful treatment between the pressing roller 10B and thepressing roller 30A of the material to be pressed, since here only areapressing and kneading effects are exerted on the material to be pressed.In this connection the large wrap angles of more than 180° created bymeans of this arrangement should again be mentioned, as well as the"free", i.e. straight, filter band sections between the respectiveoutlet roller of a pressing roller pair and the succeeding inlet rollerof the next pressing roller pair.

FIG. 5 represents a variant of the arrangement in accordance with FIG.4, wherein no pressing gaps have been set, instead the first and lastpressing roller pair is provided with a braking device B1, B2, whichleads to an increase in the band tension and area pressing in the areaof the center pressing roller pair.

FIG. 6 shows the supplement of an arrangement of three pressing rollerpairs by a drying band (also see FIG. 1) at the outlet side, which isguided on the last outlet roller 30B and in this way removes residualmoisture from the top of the upper filter band 80. A drying roller 95,which can be pressed against the underside of the filter band 90, ispivotably seated (see FIG. 1) to remove residual moisture from theunderside of the lower filter band 90. A drying band 70B, for example afelt coating, has been applied for this purpose to the drying roller 95.

FIG. 7 shows a variant of the drying roller 95, namely a drying band 70A(for example a felt band), which is wrapped from below around a partialarea of the outlet roller 30B with the aid of two reversing rollers, sothat here drying over a larger area can take place in contrast to theessentially linear contact surface of the drying roller 95.

FIG. 8 shows an arrangement with two pressing roller pairs 101A, 101B,201A, 201B, downstream of which three further pressing rollers 401, 402,403 are placed, wherein the pressing rollers 401, 402 are held on acommon pivot frame 500 (tandem roller) and the pressing roller 403 asthe outlet roller can be separately displaced and in this way a furtherpressing gap 404 can be set, however, essentially without a wrap area ofthe filter band on the outlet pressing roller 403.

FIG. 9 again shows three pressing roller pairs wherein, however, inregard to the displacement direction of the outlet pressing roller 30B,the last pressing roller pair is tilted by 90° in respect to the axis ofthe first two pressing roller pairs 10, 20, so that the angles α, drawnin here in correspondence with FIG. 2, are drawn in relation to thevertical.

Finally, FIG. 10 shows an arrangement of five pressing roller pairs, thefirst two horizontally behind each other, the last three verticallyabove each other, an arrangement which assures a particularly compactstructural shape along with a high degree of drying.

In connection with the representations of FIGS. 3 to 10, the axes andpivot arms and displacement guides are not drawn in, since variousstructural solutions offer themselves here, such as are known in theprior art.

FIG. 11 shows a preferred embodiment of the feeding station AF: anarrangement of spiral conveyors S1, S2, S3 allows a cycle of thematerial to be pressed and to be placed on the lower filter band 90,which is filled into a container B, if necessary by way of a comminutingstation (for example hammer mill H). The first spiral conveyor S1 isloaded from the container B and lies horizontally transversely above thefilter band 90. A cylinder shell cutout SV is provided at the undersideof the cylindrical shell, whose size or opening angle can be adjusted,by means of which the thickness on the filter band 90 of the layer ofmaterial to be pressed can be preset. The desired amount of material tobe pressed is placed on the filter band in accordance with this setting.In the course of this the first spiral conveyor S1 is operatedsufficiently fast so that the conveyed amount is greater than the amountfed to the filter band, so that a complete and even feeding of materialto be pressed is assured. The excess amount of material to be pressed atthe end of the feed opening SV is again fed to the container B via twofurther spiral conveyors S2, S3, so that to this extent a feed cycle isformed, which is symbolized in FIG. 11 by the arrows.

It is possible to employ other conveying units in place of spiralconveyors, for example a conveyor belt with stripping devices in placeof the first spiral conveyor S1, such as represented in FIG. 12:

In FIG. 12, conveyor belt F1 is also located transversely to theconveying direction of the filter band 90'. The container B' is locatedat the feed end of the conveyor belt F1, and the material to be pressedis fed to the conveyor belt F1 via an opening on the bottom of thecontainer B'. In this case the height HB of the opening is determined bymeans of an adjustable flap or shutter B1. A distributing panel F2 ispivotably held on the conveyor belt F1 in such a way that its openingangle γ can be adjusted in the direction toward the container B'. Thisopening angle γ and the opening height HB of the feed opening of thecontainer B' together then determine the amount of material to bepressed which reaches the filter belt 90' via a delivery panel F3.Material to be pressed, which has passed behind the panel F2, thenreaches the downstream connected spiral conveyors S2', S3', as in theabove described exemplary embodiment, and is again fed into thecontainer B'. A guide panel F4 is used to define the feeding width andprevents the placement of undesired portions of material to be pressedon the edge area of the filter band 90'.

We claim:
 1. In a device for dewatering a suspension, which deviceincludes a plurality of rollers and two filter bands for enclosing thesuspension, the two filter bands being guided along an S-shaped patharound the rollers so that each roller is contacted by one of the bandsover a respective contact area, the improvement wherein:said pluralityof rollers comprise at least one pair of rollers composed of first andsecond rollers; and said device further comprises at least onedisplacement mechanism coupled to one of said rollers of said at leastone pair, said displacement mechanism being movable to displace said oneof said rollers of said at least one pair relative to the other one ofsaid rollers of said at least one pair over a path to create a pressinggap of adjustable width between said first and second rollers and apressing force of adjustable magnitude on the suspension, wherebymovement of said displacement mechanism creates an adjustable relationbetween the dewatering produced in the pressing gap and the dewateringproduced in the contact area wherein said displacement mechanismcomprises a pivot arm supporting said first roller, means for applying adisplacement force to said first roller, and means for applying adisplacement force to said first roller for displacing said roller oversaid path, and wherein said filter bands are movable in a directionwhich causes successive portions of said bands to pass around said firstroller before passing around said second roller, and said displacementmechanism further comprises means for effecting linear displacement ofsaid second roller.
 2. The device in accordance with claim 1 whereinsaid displacement mechanism is movable for displacing said one of saidrollers relative to the other one of said rollers in order to vary thesize of at least one contact area.
 3. The device in accordance withclaim 1 further comprising two frames between which said plurality ofrollers are disposed, and said displacement mechanism is supported byone of said frames.
 4. The device in accordance with claim 3 whereinsaid frames extend along mutually parallel planes, each of said rollershas an axis of rotation, a line between the axes of rotation of saidrollers of said at least one pair forms an angle, α, with each plane,and said displacement mechanism is operable for displacing said one ofsaid rollers over a path which causes the angle, α, to be set at anyvalue between 30° and 160°.
 5. The device in accordance with claim 4wherein:said at least one pair of rollers comprises a plurality of pairsof rollers; said filter bands are guided around each pair of rollers insuccession; and said at least one displacement mechanism comprises aplurality of displacement mechanisms each coupled to one of said rollersof a respective one of said pairs of rollers and each operable forindependently displacing the one roller of its respective one of saidpairs of rollers.
 6. The device in accordance with claim 4 wherein saidfilter bands extend along a straight path portion between two of saidpairs of roller.
 7. The device in accordance with claim 5 wherein eachof said displacement mechanisms is movable to create a spacing betweensaid rollers of a respective pair of rollers, and the S-shaped pathfollowed by said filter bands between said rollers of the respectivepair of rollers has a straight section between said rollers when thespacing exists between said rollers.
 8. The device in accordance withclaim 5 wherein said plurality of pairs of rollers consists of threepairs of rollers including two outer pairs of rollers and a central pairof rollers between said two outer pairs of rollers, said rollers of saidcentral pair of rollers are positioned to provide a spacing between saidrollers of said central pair of rollers, and said device furthercomprises braking means coupled to one roller of each of said outerpairs of rollers.
 9. The device in accordance with claim 1 wherein saidfilter bands are movable in a direction which causes successive portionsof said bands to pass around said second roller, and said device furthercomprises a first movable drying band disposed for removing moisturefrom one of said filter bands while said filter bands are passing aroundsaid second roller.
 10. The device in accordance with claim 9 furthercomprising a second movable drying band disposed for removing moisturefrom the other one of said filter bands while said filter bands arepassing around said second roller.
 11. The device in accordance withclaim 10 further comprising a drying roller having an outer surfacewhich carries said second movable drying band.
 12. The device inaccordance with claim 10 wherein at least one of said drying bands is afelt band.
 13. The device in accordance with claim 1 wherein said devicefurther comprises a feeding station disposed for supplying thesuspension to said plurality of pairs of rollers, said feeding stationcomprising a hammer mill for effecting a preliminary dewatering of thesuspension.
 14. The device in accordance with claim 1 wherein said atleast one pair of rollers comprises a plurality of pairs of rollers,each of said rollers has an axis of rotation, in each of said rollerpairs, the axes of rotation extend along a line, and each line alongwhich the axes of rotation of one roller pair extends is parallel to theline along which the axes of rotation of the rollers of every otherroller pair extends.
 15. The device in accordance with claim 1 whereinsaid at least one pair of rollers consists of two pairs of rollers, andsaid device further comprises two additional rollers disposed downstreamof said two pairs of rollers with respect to the direction of travel ofsuspension through said device.
 16. The device in accordance with claim15 further comprising a connecting frame supporting said two additionalrollers.
 17. The device in accordance with claim 15 further comprising athird roller disposed downstream of said two additional rollers withrespect to the direction of travel of the suspension through saiddevice, said third roller constituting an outlet roller; and a lowerframe supporting said third roller.
 18. The device in accordance withclaim 17 wherein said third roller is mounted to be displaced againstone of said additional rollers to form a pressing gap through which saidfilter bands pass.
 19. The device in accordance with claim 1 whereinsaid two filter bands contact at least one of said rollers over an angleof at least 180°.
 20. The device in accordance with claim 1 wherein saiddevice further comprises a feeding station disposed for supplying thesuspension to said plurality of pairs of rollers, said feeding stationcomprising a plurality of conveyor units for applying suspension in aneven layer having a predetermined thickness to one of said filter bandsand for recirculating excess suspension.
 21. The device in accordancewith claim 20 wherein said conveyor units comprise a first spiralconveyor extending horizontally above said one of said filter bands,said first spiral conveyor including a cylindrical shell having a bottomportion, said cylindrical shell being provided with an adjustable cutoutlocated at said bottom portion to provide an outlet opening from saidfirst spiral conveyor.
 22. The device in accordance with claim 21wherein said feeding station further comprises a container forcontaining suspension to be dewatered, said first spiral conveyor beingdisposed for conveying suspension from said container; and a furtherspiral container disposed for returning excess suspension to saidcontainer.
 23. The device in accordance with claim 20 wherein saidconveyor units comprise a conveyor belt extending horizontally above oneof said filter bands; and a stripping element disposed above saidconveyor belt for controlling delivery of suspension to said filterbands.
 24. The device in accordance with claim 23 wherein said feedingstation further comprises a container for containing suspension to bedewatered, said container having an outlet opening of adjustable size.25. The device in accordance with claim 23 wherein said filter bands aremovable in a direction relative to said feeding station, said strippingelement has an end which faces away from said container and saidstripping element is mounted for pivotal movement about the end whichfaces away from said container to vary an angle between said strippingelement and the direction in which said filter bands are movable.